Electron discharge furnace for heating conductive rods



ELECTRON DISCHARGE FURNACE FOR HEATING CONDUCTIVE RODS Filed April 6. 1962 A. L. DONLEVY I May 3, 1966 2 Sheets-Sheet l I5 Fig.3.

INVENTOR. Alfred L. Donlevy 2 Sheets-Sheet 2 Fig.8. 8O

A. L. DONLEVY ELECTRON DISCHARGE FURNACE FOR HEATING CONDUCTIVE RODS 24 v Ac Cur re m 2000 V Constant May 3, 1966 Filed April 6, 1962 INVENTOR. Alfred L. Donlevy United States Patent 3,249,797 ELECTRUN DISCHARGE FURNACE FOR HEATING CONDUCTIVE RODS Alfred L. Donlevy, San Leandro, Calif., assignor to Stanifer Chemical Company, New York, N.Y., a corporation of Delaware Filed Apr. 6, 1962, Ser. No. 185,639 6 Claims. (Cl. 31569) This invention relates to an improved electron beam gun for electron discharge furnaces for heating conductive rods.

In analyzing metallurgical properties of highly purified refractory metals it is necessary to provide a concentrated heat source which will uniformly elevate the temperature of a. metal sample under conditions which will allow a predetermined or controlled stress to be applied to the metal. With such a device the stress rupture data can be accumulated which will allow statistical, metallurgical and mechanical characteristics to be determined.

An electron beam source is an ideal source of energy for this purpose. The electron beam type of heater operates in an extremely high vacuum which affords an atmosphere in which heat radiation and conduction are held at an absolute minimum. The high vacuum also prevents any ambient contamination such as would normally occur in an atmosphere containing oxygen, carbon or other im purities which might affect the metallurgical characteristics.

The principal object of this invention is in providing a novel electron gun assembly for such a test furnace which will efficiently radiate thermal energy uniformly throughout the cross-section of the test area of the metal test member.

In the electron gun assembly of this invention there is provided a generally cylindrical cathode housing closed at the top and bottom and providing in the center of the top and bottom apertures arranged to receive an elongated length of the test material which is held under tension in substantially axial alignment with the cylindrical cathode housing. Thermally emissive filaments are mounted on the interior of the cathode housing and spaced therefrom to emit electrons which heat the elongate test material by electron bombardment.

A feature and advantage of this invention lies in the fact that the cylindrical cathode housing functions as a focusing mechanism to direct and focus the electrons emanating from the filament in a controlled evenly distributed pattern to the test materialanode.

Another feature and advantage of this invention lies in the fact that the cathode housing also provides an electron beam shield which restricts the passage of electrons and radiation exteriorly of the cathode housing thus protecting the vacuum chamber and various mounting members within the vacuum chamber from spurious electron bombardment and radiation.

A still further feature and advantage of this invention lies in the fact that gas from the interior of the cathode housing is withdrawn from the top and bottom apertures in which the test anode is located. Because the test anode is at high positive potential it is extremely difficult for electrons to escape through the gas withdrawing port.

A still further object of this invention is to provide an electron gun in which filaments are symmetrically placed within the inner surface of the focusing cathode housing so that the result in radiation pattern is evenly directed to all parts of the specimen or test anode and the electrostatic field set-up between the focusing cathode and the anode continuously influences the electrons emitted from the filament to cause an inward radial acceleration and resulting increase in radial velocity because of both an increase in field potential and field density in the direction of the anode.

Another object of this invention is to provide a cylindrical electrical field which acts on electrons emitted from some areas of the filaments to cause them to acquire a constant velocity vector in the annular direction and an increasing electron velocity vector in the inward radial direction.

A feature and advantage of this result lies in the fact that the electrons will strike the surface of the anode in an evenly distributed array and in a direction substantially normal to the surface of the electrode.

A still further object of this invention is to provide an improved electron gun having an interior elongate anode and a concentric focusing cathode housing surrounding the anode in enclosed relationship with thermally emissive elongate channels aligned with the anode and symmetrically placed on the interior of a cathode housing in spaced relation therefrom to create a group of aligned electron beam emanating sources which will evenly bombard the anode throughout the entire length of the test area.

Other objects of the present invention will become apparent upon reading the following specification and referring to the accompanying drawings in .which similar characters of reference represent corresponding parts in each of the several views.

In the drawings:

FIG. 1 is a perspective view of the cathode housing of this invention.

FIG. 2 is a view similar to FIG. 1 showing the segmented section of the housing removed therefrom.

FIG. 3 is a cross section diagrammatic view showing the furnace structure with the electron gun assembly contained therein.

FIG. 4 is a cross-sectional view of the furnace structure with the gun mounted therein showing the electrical connections to the elements therein in schematic form.

FIG. 5 is an interior view showing the mounting of one of the filaments.

FIG. 6 is a cross-sectional view showing the opposite filament.

FIG. 7 is a diagrammatic view showing the electron flow path from the filaments to the anode and illustrative lines representing the electrostatic field.

FIG. 8 is an internal sectional view showing an alternative embodiment of the filament structure in which the filaments are mounted in direct vertical parallel alignment.

The test furnace generally comprises a sealed evacuated outer chamber A forming the vacuum chamber. A cylindrical focusing cathode housing B is mounted internally of the chamber and carries an elongate test specimen C in axial alignment with the cathode. The test specimen may be formed of any conductive metal capable of functioning as an anode. The test specimen is heated in the area within the cylindrical cathode by electrons emitted from a plurality of filaments or emitters 12 and 12 mounted on the interior walls of the cathode housing B. The cathode housing is at equal potential with the filaments of emitters 12 and 12 and functions to focus electrons toward the test specimen or anode C and as a shield to prevent spurious electrons from straying outside of the cathode housing.

Chamber A is evacuated by conventional means such as by using a pump 13 in fluid communication with the chamber by a passageway l4.- The vacuum in the chamber should be maintained below .1 micron of mercury and preferably within a range of between .1 to .01 microns of mercury although lower pressure will work quite adequate but are usually not necessary and are costly to maintain.

The elongate test anode or specimen C is located in axial alignment within the cathode housing B and is held under stress by a pulling block 15 holding the top end 16 of the test specimen and a bottom anchor 17 which engages the bottom end 18 of stock or test specimen C.

Stress is applied by an hydraulic or pneumatic pulling mechanism generally indicated at 20 which is arranged to pull block 15 under high pressure. The pulling mechanism is of conventional design and is arranged to provide enough force to exert rupturing stress on the stock material.

A fluid seal 21 engages the sliding block 15 so that an adequate vacuum can be maintained within chamber A. Thus by this mechanism test specimen C can be subjected to any predetermined or calculated stress while being completed contained within evacuated chamber A.

Cathode housing B is supported by legs 22 mounted on the bottom of chamber A and insulated from electrical contact with the bottom by insulators 23 so that the entire cathode housing B is supported in electrical insulation from the body of chamber A.

Electron gun or cathode housing B is formed with a generally cylindrical wall 25 having a top plate 26 and a bottom plate 27. Both top plate 26 and bottom plate 27 are formed with axially aligned apertures 28 and 29 adapted to receive test structure or anode C and of sufficient dimension so that there is a sufficient space between the anode and the top and bottom plates 26 and 27 respectively to insure that there will be no electrical contact between test stock anode C and cathode housing B.

Cylindrical side wall 25 and top and bottom plates 26 and 27 are segmented in a generally pie shaped segment generally indicated at 30 which can be removed to provide free access into the cathode housing. Segmented section 30 is formed with a top wall 31 which overlies the top plate 26 to provide support for the segmented section when it is inserted in place. The side wall 32 of the segmented section is arranged with an inside diameter the same as the remainder or cylindrical member 25 so that when the segmented section 30 is in place the side wall 32 completes the cylinder. A bottom wall 34 is affixed to the segmented section 30 to complete the closure of the bottom plate 27. It can thus be seen that the segmented section 30 can be inserted to form a completely enclosed cylindrical housing and can be removed to provide an area into which stock or anode C can be inserted. The removable segment 30 also allows access into the interior of cathode housing B for maintance and adjustment of the electrical elements on the interior of the housing.

Chamber A is provided with an exterior door 38 which is hinged at 39 so that it may be opened in order to gain access into the chamber. Door 38 is in alignment with the segmented section 30 so that when the door is open free access into the gun through the door is available.

Cathode housing B can be cooled by placing water coils on the exterior of the housing in a conventional manner.

A window 40 is cut in side wall 32 and a quartz window 41 is formed in the side wall in door 38. The two windows 40 and 41 are in alignment with each other and test anode C so that the anode can be observed during testing.

Conventionally in such test apparatuses electronic means are used to optically measure thecolor temperature of the metal of test anode C during heating which is a direct analogue of the heat. Thus by optical observation of the anode through windows 40 and 41 an accurate gage of temperature is obtained.

The interior of cathode housing B is formed with the two filament structures indicated at 12 and 12 The filament structure 12 is mounted by standoff insulators 42, 43 and 44 to carry the filament in substantially spaced relation to the inside wall of cathode housing B. Filament 12 is formed in a generally V-shaped configuration with the two insulators 42 and 44 being located adjacent the top portion of the housing spaced apart approximately and the central insulator or support 43 is mounted midway between the two insulators 42 and 44 on the lower portion of the inner wall of the cathode housing. Filament 12 constitutes a solid tungsten wire continuously mounted from insulator 42 to insulator 43 and thence extending up to insulator 44. The insulators 42 and 44 carry an electrical conductor to form electrical connection to the top portion of the filament to form external contacts 45 and 46 on the exterior of cathode housing B to which electrical connections can be made.

Filament 12 is supported by three standoff insulators 48, 49 and 50 in which the two insulators 48 and 50 are mounted on the bottom portion of the inside wall of the cathode housing in spaced apart relation and the insulator 49 is located adjacent the top in such a way that the insulators 48, 49 and 50 support the continuous tungsten filament 12 in an inverted V-shaped configuration. Thus the filament 12 has its apex on the bottom portion of the housing and filament 12 has its apex on the top of the housing.

Filament 12 has two terminal connectors 51 and 52 passing through insulators 48 and 50 respectively forming the terminal connections exterior of the housing.

The electrical connections to the filaments include two cables 60 and 61 which connect to the two terminals 45 and 51 respectively which connect to one leg of a 24 volt A.C. power supply generally indicated at 63. The opposite leg of line 64 from power supply 63 is connected directly to the body of cathode housing B. Terminals 46 and 52 likewise are connected directly to the body of cathode housing B so that the filament heater voltage passes from terminals 45 and 51 respectively through filaments 12 and 12 to the body of the cathode housing.

The B-plus supply for the gun is derived from a constant current DC power source generally indicated at 68. The negative leg 69 from constant current power supply 68 is applied directly to the cathode housing and the positive leg 70 is connected to chamber A and to anode C through the sliding block assembly 15 and the bottom or anchor connection 17.

It can thus be seen that by this circuit the filaments 12 and 12 are energized with A.C. heater current and with high negative constant current voltage. It can also be seen that the entire cathode housing is at the same negative potential as the two filaments 12 and 12 while the anode C is at high positive potential.

By virtue of this structure the heated filament will emit electrons which will be attracted to high positive anode C to cause the anode to heat. Because the cathode housing including the cylindrical wall and top and bottom plates 26 and 27 are at high negative potential there will be an electrostatic field build up completely enclosing the emission area forming a generally repelling force tending to deflect electrons emitted from the two filaments 12 andd12 away from the housing walls and toward the ano e.

Cylindrical walls 25 actually perform a focusing function tending to create a diffused electron bombardment pattern so that the entire surface of anode C is subjected to substantially equal bombardment. This is an important factor in stress rupture furnaces of this type in that it is necessary that all portions of the test anode through the test cross-sectional areas be heated uniformly in order to obtain meaningful stress rupture analytical data. The very nature of the circular electrostatic field focusing and diffusing electron beam paths is in such a way that such even bombardment is obtained. It is also noted that housing B completely encloses the anode test area so that the electrostatic field prohibits electron flow from traveling to positive housing A. Thus the cathode housing forms a shield preventing destructive electron bombardment of the chamber assembly A and performs the function of focusing electron distribution to the test anode in an evenly dispersed pattern. The even dispersion of the pattern is also further accomplished by the inverse structure of the two filaments 12 and 12 in which their apices are facing in opposite directions so that the total emission throughout the length to the rod of the test anode C is substantially equal.

Filaments 12 and 12a are spaced inwardly from the walls of cathode housing B sufficiently so that the electrostatic field imposed upon the cathode housing will'not unduly restrict electron emission from the filaments and also far enough from the anode so that there will not be a reduction in voltage between the filaments and the anode.

It is noted that the device is powered in its B-plus by a constant current power source. Should the test material have any impurities which might be outgassed during heating a plasma would be created between the filaments and the anode. The plasma would effectively decrease the impedance between the filament and the anode which would in turn decrease the voltage between the two electrodes. Decrease in voltage would decrease the power and thus by the use of a constant current power supply a state of equilibrium is obtained even under conditions of some outgassing of the test material of anode C.

Apertures 28 and 29 and the spacing between the electrode C affords a suflicient area through which the gas within the chamber can be evacuated through the pump action of pump 13. It is also noted that the only substantial opening to the cathode is around the anode structure which is at high positive potential so that any electrons which might pass through the aperture would be first attracted to the nearest positive area which is the anode itself thus providing a gas escape for the cathode which will entrap and prevent electron bombardment from passing outside through the gas escape port.

It is further pointed out that the electrons emitted by the filaments have a negative potential which are attracted toward the positive anode C. When the electrons leave the surfaces of the filaments they have a low initial velocity. However, the force of the electrostatic field effected by cathode housing B accelerates the electrons in an inward radial direction causing them to increase in velocity as they approach the anode. The direction of electron How is illustrated in FIG. 7 which illustrates a series of annular equipotential fields represented by the lines El, E2, and E3. The imaginary lines represent paths of equal electrostatic field potential.

A certain percentage of the electrons emitted from a filament 12 will have the velocity vector both radial and tangential to anode C due to the influence of the negative space charge created by the density of other electrons leaving the surface of the filament. Some of these electrons will move toward focusing cathode B. However, the electrostatic field of the cathode housing will continuously accelerate them toward the anode and they will prescribe a pattern such as indicated by dotted line 75.

Any electrons which acquire a velocity vector in the concentric or annular direction will retain their velocity without being substantially affected by the field effects. However, as it can be seen any radial velocity vector in the same plane as the electrostatic field direction will be effected by the field and moved in a curved path in the annular direction of constant velocity and in an increasing velocity toward anode C. The effect of the field is to focus the electrons toward anode C in such a way as to strike the anode in a more perpendicular attitude. It is noted also that the filaments extend throughout the length of the test area of the anode so that substantially equal electron emission will take effect throughout each cross-sectional area of the anode throughout the test area.

The filaments have heretofore been described as shown in FIGS. 5 and 6 as being formed in inverted V-configurations. However, it is believed obvious that the filaments can be formed in equidistantly spaced vertical positions as indicated in FIG. 8. Each of the filaments 79 in the embodiment as shown in FIG. 8 is held in spaced relation to the side walls of the chamber by suitable standoff insulators as indicated at 80. The filaments 79 are spaced equidistantly apart so that if there are four such filaments they will be placed at intervals about the inside of the cathode housing. The filaments in this embodiment are in complete mechanical alignment with the test structure and dlue to their 90 placement form an even radiation pattern about the entire circumference of the test material.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is understood that certain changes and modifications may be practiced within the spirit of the invention as limited only by the scope of the appended claims.

I claim:

11. An electron gun assembly for heating a substantially elongate conductive anode member contained within an evacuated chamber, comprising a conductive cylindrical member mounted around said elongate anode member having a closed apertured top and bottom, the aperture formed by the top and bottom being aligned with the elongate anode member to space the top and bottom in electrical isolation from the elongate anode member, thermally emissive filament members mounted on the inside of said cylindrical member, said filament members extending from the top of said cylindrical member to the bottom of said cylindrical member and :being spaced inwardly from the wall of said cylindrical member and in spaced relation to the elongate anode member, means imposing a filament heater current to said filament members to cause the filament members to heat to electron emission temperature, and means applying a high positive potential to the elongate anode member and a high negative potential to both said filament members and said cylindrical member.

2. An electron gun assembled according to claim 1 and wherein said means applying said high negative and positive potential constitute a source of substantial constant current.

3. An electron gun assembly for heating a substantially elongate conductive anode member comprising an evacuated chamber, said elongate anode member being mounted within said chamber, a conductive cylindrical cathode housing mounted around said elongate anode member with the elongate anode member being in axial alignment in the center of said housing, said housing having a closed a'pertured top and bottom in which the apertures in the top and bottom are axially aligned to receive the elongate anode member, said elongate member projecting through the apertured top and bottom of the housing and extending exteriorly on both ends outside of said housing, the aperture formed by the top and bottom of the housing being sufficiently large to prevent any electrical'contact between said elongate anode member and said housing, thermally emissive filament members mounted on the inside of said housing in substantially axial aligned relationship with said elongate anode member, means imposing a filament heater current on said filament members to cause the filament members to heat to electron emission temperature, and means applying positive potential to the elongate anode member and a high negative potential to 'both said filament members and said housing.

4. An electron beam gun for heating an electrically conductive test specimen while it is under mechanical stress conditions in a vacuum chamber the improvement comprising an electrically conductive enclosure having a cylindrical Wall which surrounds said test specimen in spaced relation, said enclosure having an apertured top and bottom through which said test specimen can project interiorly from said enclosure in electrical isolation, filament means mounted on the inside of said enclosure intermediate of said cylindrical wall and spaced in substantially parallel alignment with said specimen, means heating said filament means to emit electrons, and means applying a negative electrical potential to said enclosure and a 'positive potential to said specimen to create an electrostatic field which focuses electrons emitted from said filament to said specimen.

5. An electron gun assembly for heating a substantially elongate conductive member comprising an evacuating chamber, a conductive cylindrical member mounted within said chamber and in spaced relation to said chamber, said cylindrical member having a closed top and bottom formed by conductive plates, said top and bottom plates being centrally apertured, said elongate conductive anode member being positioned through the center point of said cylindrical member with both ends of the elongate member passing through the apertures formed by the top and bottom plates and spaced therein out of electrical contact with said plates, said cylindrical member being formed with a removable segment including a portion of the side wall of the cylindrical member and portions of said top and bottom plates, the removable segment of said top and bottom plates opening to the aperture formed therein, and thermally emissive filament members mounted on the inside of the non-removable portion of said cylindrical member and extending from the top of said cylindrical member to the bottom of said cylindrical member, means imposing a filament heater current to said filament member to cause the filament members to heat to electron emission temperatures, and means applying a high positive potential to the anode member and a high negative potential to both said filament members and said cylindrical member.

6. An electron gun assembly for heating a substantially elongate conductive member comprising an evacuating chamber, a conductive cylindrical member mounted within said chamber and in spaced relation to said chamber, said cylindrical member having a closed top and bottom formed by conductive plates, said top and 8 bottom plates being centrally apertured, said elongate conductive anode member being positioned through the center point of said cylindrical member with both ends of the elongate member passing through the apertures formed by the top and bottom plates and spaced therein out of electrical contact with said plates, said cylindrical member being formed with a removable segment including a portion of the side wall of the cylindrical member and portions of said top and bottom plates, the removable segment of said top and bottom plates opening to the aperture formed therein, thermally emissive filament members mounted on the inside of the non-removable portion of said cylindrical member, means holding said filament members spaced inwardly from the inside of said cylindrical member a sulficient distance to allow electron emission to occur about the filament members from all sides when said filaments are heated to electron emission temperatures and spaced sufliciently from said anode member to create a high impedance spacing between said filament members and said anode member, means imposing a filament heater current to .said filament member to cause the filament members to heat to electron emission temperatures, and means applying a high positive potential to the anode member and a high negative potential to both said filament members and said cylindrical member.

References Cited by the Examiner UNITED STATES PATENTS 2,809,905 10/1957 Davis et al 2l9-----l2l 3,020,387 2/1962 Basche et a1. 219- FOREIGN PATENTS 803,746 10/1958 Great Britain.

GEORGE N. WESTBY, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

1. AN ELECTRON GUN ASSEMBLY FOR HEATING A SUBSTANTIALLY ELONGATE CONDUCTIVE ANODE MEMBER CONTAINED WITHIN AN EVACUATED CHAMBER, COMPRISING A CONDUCTIVE CYLINDRICAL MEMBER MOUNTED AROUND SAID ELONGATE ANODE MEMBER HAVING A CLOSED APERTURED TOP AND BOTTOM, THE APERTURE FORMED BY THE TOP AND BOTTOM BEING ALIGNED WITH THE ELONGATE ANODE MEMBER TO SPACE THE TOP AND BOTTOM IN ELECTRICAL ISOLATION FROM THE ELONGATE ANODE MEMBER, THERMALLY EMISSIVE FILAMENT MEMBERS MOUNTED ON THE INSIDE OF SAID CYLINDRICAL MEMBER, SAID FILAMENT MEMBERS EXTENDING FROM THE TOP OF SAID CYLINDRICAL MEMBER TO THE BOTTOM OF SAID CYLINDRICAL MEMBER AND BEING SPACED INWARDLY FROM THE WALL OF SAID CYLINDRICAL MEMBER AND IN SPACED RELATION TO THE ELONGATE ANODE MEMBER, MEANS IMPOSING A FILAMENT HEATER CURRENT TO SAID FILAMENT MEMBERS TO CAUSE THE FILAMENT MEMBERS TO HEAT TO ELECTRON EMISSION TEMPERATURE, AND MEANS APPLYING A HIGH POSITIVE POTENTIAL TO THE ELONGATE ANODE MEMBER AND A HIGH NEGATIVE POTENTIAL TO BOTH SAID FILAMENT MEMBERS AND SAID CYLINDRICAL MEMBER. 